The Elements of Moral Science (1835, 1856 ed.)
Duties Which Arise from the Constitution of the Sexes
1. The subject upon which we now enter presents a striking illustration of the truth of these remarks. On the one hand, it is evident that the principle of sexual desire is a part of the constitution of man. That it was intended to be gratified is evident from the fact that without such gratification the race of man would immediately cease to exist. Again, if it were not placed under restrictions, that is, were promiscuous intercourse permitted, the race would perish from neglect of offspring and universal sterility. Thus universal celibacy and unlimited indulgence would both equally defeat the end of the Creator. It is, therefore, as evident that our Creator has imposed a limit to this desire as a part of our constitution, as that he has implanted within us the desire itself. It is the object of the law of chastity to explain and enforce this limit.
2. As it is manifestly the object of the Creator that the sexes should live together and form a society with each other in many respects dissimilar to every other society, producing new relations and imposing new obligations, the laws of this society need to be particularly explained. This is the law of marriage.
3. As the result of marriage is children, a new relation arises out of this connection, namely, the relation of parent and child. This imposes special obligations upon both parties, namely, the duties and rights of parents, and the duties and rights of children.
This class of duties will therefore be treated of in the following order: